1. Field of the Invention
This invention relates to a printed circuit board, and more particularly, the invention relates to a primary functional circuit board, which is designed in a simple structure and can be used to verify the chip function by an alternative manner.
2. Description of Related Art
In the high technology industry, the design of the integrated circuit (IC) plays an important role. Referring to FIG. 1, it is a drawing, schematically illustrating the conventional primary functional circuit board implemented with an IC. So called, the primary functional circuit board refers to a circuit substrate board with the specific function, such as the graphics card, sound card, network card or the mother board of the computer, in which the circuit substrate board has been implemented with a processor capable of the specific control function. Particularly, it can include the devices such as a basic input/output system (BIOS), a firmware device, or other function devices. From the structural point of view, the functional circuit board can include the circuit board 100 and the chip 150. The circuit board 100 can be implemented with a number of electronic devices (not shown in FIG. 1), which form a circuitry controlled by the chip 150, so as to perform the requested function for the primary functional circuit board. In other words, we can treat the chip 150 as a key part of the data transmission and the control in the primary functional circuit board.
The chip 150 is incorporated with the firmware program, which has the complex function to be able to execute the instruction of the primary functional circuit board. Since the function of the chip 150 is rather complex and an add or remove of the function may be required by the user after mass production, the firmware program often needs to be modified, by making use of the property of the field programmable gate array (FPGA), and also use of the programmable chip to control the circuit under control on primary functional circuit board. Then it needs to check whether or not the primary functional circuit board has satisfied the design requirement. In this situation, if the chip 150 or the firmware program in external connection has a defect in design, then the engineers can further edit the FPGA as necessary. The firmware program after modification can then be burned into the programmable chip again to see whether or not an improvement is obtained. By using the foregoing procedure to continuously modify and test, the program for the FPGA can be set at the end. Then, the chip can be fabricated according to the considerations of the program and the possible requirement from the user in the future. As a result, the design requirement for the primary functional circuit board can be satisfied, so as to take the place of the chip 150, which has high fabrication cost, occupies much valuable space on the printed circuit board, and needs to be modified by the programmer, as well as the external read only memory (ROM).
From the foregoing description, when the FPGA program still needs to be tested repeatedly, the engineer can continuously modify the content in the programmable chip until the function operation can be assured in normal operation. Then, according to the FPGA program, the final version is used to fabricate the chip. This chip then can effectively take the place of the original chip 150 as well as the firmware program stored in the internal ROM or the firmware program stored in the external ROM, so as to achieve a more compact and cheaper product. Then, the present invention provides a method for using the sub-board associating with the FGPA and executing all of the primary function for the original chip 150 associating with the ROM on the reserved functional pins for the common connection, so as to offer easier verification of the function and the judgment of a correct or erroneous case in design.